Electron discharge device



June 19, 1962 P. RUDNICK ETAL 3,040,177

ELECTRON DISCHARGE DEVICE Filed Jan. 16, 1956 INVENTORS. PAUL RUDNICK 8| RICHARD K. ORTHUBER ATTORNEY United States Patent Ofiice 3,040,177 Patented June 19, 1962 3,040,177 LECTRUN DISCHARGE DEVICE Paul Rudnick and Richard K. Orthuher, Fort Wayne,

Ind., assignors to International Telephone and Telegraph Corporation Filed Jan. 16, 1956, Ser. No. 559,143 4 Claims. (Cl. 250-213) This invention relates to electron discharge devices and is particularly directed to an electron gun for furnishing an electron beam in a cathode ray tube.

In one type of image tube for converting an infra-red image to a visible image, there is provided a phosphorplate closely parallel to a photoconductive control screen. The photoconductive screen comprises a backing of conductive metal mesh coated on one side with a material whose conductivity changes when irradiated by infra-red light so that the electrical potential of elemental areas of the screen, corresponding to picture elements, charges different and discrete amounts. When the screen is bombarded with a collimated flood electron beam, the electrons will pass through or be reflected by elemental areas of the screen at various electrical potentials, so that the phosphor-plate is bombarded with an electron image corresponding to the incoming infra-red image. The result is a visible image on the phosphor corresponding to the invisible infra-red image projected on the photoconductive control screen. Image converters of this type may be used for converting an image of any predominate wavelength to another wavelength, by choice of the proper photoconductive material and the proper phosphor.

Unfortunately, in order to obtain appreciable electron emission, the usual thermionic cathode from which the flood beam may be obtained must be heated to a temperature Where it is visibly red. Hence, the flood cathode, heretofore, has irradiated the photoconductive screen with infra-red and visible light and thereby reduced the contrast or signal-to-noise ratio in the desired image.

The object of this invention is an image tube in which the desired image received on the photoconductive screen is not reduced in contrast by radiation from the thermionic cathode in the tube.

The object of this invention is attained by an envelope containing the flood beam thermionic cathode, a photoconductive control screen and a phosphor-plate. The cathode is hidden or out of sight from all points on the screen. Means are provided for bending the electron beam at low velocity near the cathode with a pair of small electromagnetic deflection coils to redirect the beam toward the screen.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing, wherein:

The single FIGURE of the drawing is a longitudinal sectional View of one image tube embodying the features of this invention.

The envelope of the image tube of this invention encloses the phosphor-plate 11, photoconductive control screen 12, the accelerator and collector screen 13, and the electron gun structure 14. The envelope may be of metal, as shown, closed at the lower end with the glass portion of good light transparency so that a visible image on the inner surface of phosphor-plate 11 may be viewed. If desired, the phosphor coating on the inner surface of plate 11 may be applied directly to the inner surface of the glass portion 15 of the envelope. One typical phosphor coating is zinc orthosilicate. Through window 16' and through an optical system, not shown, the infra-red image to be converted is focused and projected onto the photoconductive screen 12.

in the particular tube structure shown, the glass and metal portions of the tube are joined in conventional glass-to-metal seals. The phosphor-plate 11, photoconductive screen 12, and collector screen 13 are supported upon metal ring 17 sealed on opposite faces to the glass and metal portions of the envelope. Ceramic rods 18 electrically insulate and support the phosphor-plate 11 and photoconductive screen 12 from the collector screen 13 and the supporting plate 17.

The particular electron gun shown comprsies a metal housing 20 with an aperture at one end for passing electrons emitted from the end of cathode sleeve 21. Anode aperture plate 22 which is insulated from the housing 20 is so located and sized and operated at such a potential that the electrons emitted by the cathode are allowed to diverge somewhat into a flood beam, which is later collimated by electron lens action between the collector screen 13 and the wall It The velocity of the electrons is relatively low adjacent such an electron gun.

According to an important feature of this invention, the electron gun structure is oriented in the envelope so that the heated parts of the cathode, including the emit ting end, are out of line-of-sight with all points on the photo-conductive screen. To bend the beam so as to cover with a uniform flood of collimated electrons the entire area of the collector and the photoconductive control screen, the axial bore of the deflecting coil assembly 30 is placed to receive and deflect the beam. The opening through the deflection coil is so oriented as to redirect the beam from the electron gun 14 through the opening 31 in the light opaque partition 32 between the two regions of the envelope. If the electron beam at the aperture of the electron gun is at an angle of, say, 60 degrees from the tube axis, the deflection coil opening of coil 3!} should be placed at about 30 degrees from the tube axis, by way of example. At the low velocity of electrons they are easily deflected into their desired direction by the coil 30. An iron yoke or sleeve 33 is preferably telescoped over the coil to minimize disturbance of the beam from outside sources and to localize the magnetic field. The shield 34 attached to the envelope and around the aperture 31 will further define the limits of the electron flood beam as well as extend the light shield for the cathode. Variation of current to the coil 30 provides convenient controlling means for the beam deflection. Alternatively, small permanent magnets may be substituted for the electromagnets. Once the electrical and mechanical parameters of the tube at established, the tube can easily be reproduced in manufacture. All interior metal surfaces of the enevlope except window 16 should be blackened with an electrically conducting coating to absorb light and infra-red rays from the cathode. Carbon coating, for example, would eifectively absorb almost all infra-red radiation directed to those surfaces.

In operation, an infra-red image is projected through window 16 upon the photoconductive control screen 12 and by proper use of the electron gun 14 and deflection coils 31} the entire photoconductive screen is flooded with a collimated beam of electrons. Suitable potentials are applied to the photoconductive screen backing and to the collector screen with respect to the cathode 20, so that areas of the photoconductive screen which are in highlight portions of the image are held at a somewhat positive potential with respect to the flood cathode and permit the flood electrons to pass through to the phosphor-plate 11. Thus, the infra-red image from window 16 becomes visible on the phosphor-plate 11. The shadow areas of the image are not irradiated by any light of any wavelength from the image or the cathode, thus preserving locally the very high electrical conductvity, and hence the lightto-dark contrast among picture elements of the original infra-red image.

While the principles of the invention have been described in connection With specific apparatus, it is to be clearly understood that this description is made only by Way of example and not as a limitation to the scope of the invention.

What is claimed is:

1. A direct viewing image converter tube comprising: an enclosing envelope having a phosphor viewing plate; a photoconductive electron permeable screen in said envelope spaced from said photoconductive screen; said envelope having means for admitting a radiation image for impingement upon the one side of said screen remote from said plate; means in said envelope including a cathode for flooding said one side of said screen with low velocity electrons simultaneously with impingement of said image thereon whereby said electrons pass through said screen and onto said plate being modulated responsive to said radiation image on said screen so that an optical image corresponding to said rediation image is produced on said viewing plate, said cathode being displaced out of the line of sight from said one side of said screen; and electron deflecting means for directing said flood electrons from said cathode onto said one side of said screen.

2. An image converter tube comprising: an enclosing envelope having a photoconductive electron permeable electrode therein; said envelope having means for admitting a radiation image for impingement upon one side of said electrode; means in said envelope for generating a flood beam of low velocity electrons and for directing the same along a line away from said one side of said photoconductive electrode; an opaque partition in said envelope extending across all lines of sight between said one side of said photoconductive electrode and said beam generating means, said partition having an aperture formed therein out of the line of sight between said beam generating means and said photoconductive electrode and ofiiset from said beam line; and means for deflecting said beam through said aperture and onto said one side of said photoconductive electrode whereby said beam passes through said electrode and is modulated responsive to said radiation image thereon.

3. A direct viewing image converter tube comprising: an enclosing envelope; a phosphor viewing plate in said envelope, said envelope having a window formed therein for transmitting a visible image from said plate; an electron permeable photoconductive control screen in said envelope spaced from said plate, said envelope having another window formed therein for transmitting an incoming radiation image onto said screen on the one side thereof remote from said plate; a thermionic cathode in said envelope for generating a flood beam of low velocity electrons; an opaque partition in said envelope between said cathode and said one side of said screen, said partition having an aperture formed therein aligned with said screen, said cathode being displaced from a straight line extending from said screen through said aperture, and means for deflecting said beam from said cathode through said aperture onto said one side of said screen whereby said beam passes through said screen and onto said plate being modulated responsive to the said radiation image on said screen so that an optical image corresponding to said radiation image is produced on said viewing plate.

4. A direct viewing image converter tube comprising: an enclosing envelope; a planar electron permeable photoconductive control electrode in said envelope, the elemental areas of said electrode being individually responsive to irradiation by elements of a radiation image to produce discrete electrical potentials in each elemental area; a planar phosphor viewing plate adjacent said control electrode and coextensive therewith for providing an optical image responsive to impingement of electrons thereon; said envelope having a window formed therein for transmitting a radiation image onto the one side of said control electrode remote from said plate; a thermionic cathode in said envelope spaced from said one side of said electrode; means for preventing irradiation of said electrode by radiation from said cathode to which said electrode is responsive, said means comprising an opaque partition in said envelope between said cathode and said one side of said electrode, said partition having an aperture formed therein displaced from the straight line extending between said cathode and said electrode; and means for deflecting said beam through said aperture and onto said one side of said electrode whereby said beam passes through said electrode and onto said plate being modulated responsive to said radiation image on said screenso that an optical image corresponding to said radiation image is produced on said viewing plate.

References Cited in the file of this patent UNITED STATES PATENTS 2,277,246 McGee et al Mar. 24, 1942 2,322,361 Iams June 22, 1943 2,617,060 De Gier Nov. 4, 1952 2,683,832 Edwards et a1. July 13, 1954 2,717,971 Sheldon Sept. 13, 1955 2,798,179 Sheldon July 2, 1957 2,817,781 Sheldon Dec. 24, 1957 FOREIGN PATENTS 1,084,262 France Jan. 18, 1955 

